This invention relates to a device for preventing an image of a printing master from being printed in an inclined position on copies produced from the printing master in a duplicating apparatus.
In an offset duplicating apparatus or mimeograph, ink is applied to a plate or stencil to form thereon an ink image so that the plate or stencil may serve as a printing master, and a large number of copies are produced from the printing master by transferring the ink image to copy sheets. When such printing master is prepared, the image formed thereon may deviate from the regular position and become inclined with respect to the longitudinal center axis of the plate or stencil (inclined image printing master). Even if the image of the master plate is disposed in the regular position, the printing master may become inclined when mounted in a printing position. If this is the case, all the images printed on copy sheets from the printing master will be inclined with respect to the longitudinal center axis of the copy sheets. This is not desirable because such copies are not acceptable, particularly when the images printed on opposite sides of a copy produced from the printing master are inclined or when a number of copies each having inclined images on opposite sides are bound into a book form.
In one device known in the art for preventing the formation of an inclined image on copies produced from a printing master, an inclined image printing master is caused to be inclined to compensate for the inclination of the image when the printing master is mounted on a master cylinder, so that the image on the printing master can be brought into contact with a copy sheet in the regular position.
In this device, adjustments of the position of the printing master on the master cylinder to compensate for the inclination of the image on the printing master should be effected several times, because it is impossible to ensure correct positioning of the printing master in one operation. Thus, with this device, it has been necessary to remove the ink applied printing master from the master cylinder and mount the same thereon again after interrupting the operation of the duplicating apparatus. This is troublesome and time consuming. Additional disadvantages are that the printing master tends to become wrinkled or damaged, and that the hands of the operator get soiled with ink.